WASHINGTON D.C. - The U.S. Supreme Court will not hear Brendan Dassey's appeal, it was announced Monday.

No explanation was given for the decision. Four of the nine Supreme Court justices must agree to accept a case.

It is a crushing blow for Dassey, who is fighting his conviction in the 2005 homicide of photographer Teresa Halbach. He sought review by the Supreme Court after lower courts overturned then ultimately reinstated his conviction. At the heart of this case is his confession — and heated debate over whether it was voluntary or coerced by investigators.

Dassey and his uncle, Steven Avery, were sentenced to life in the Wisconsin prison system for Halbach's murder. Dassey is eligible for extended supervision in 2048.

Avery is also fighting his conviction. Their cases have gained international attention since the release of the Netflix docu-series "Making a Murderer" in December 2015.

His attorneys argued in their petition that Dassey — who was 16 years old when he was questioned by police and had limited intellectual abilities — falsely confessed to the brutal crime under coercive pressure by investigators. But even larger than Dassey, they argued, is that lower courts are merely noting a defendant's age and mental capabilities instead of deeply analyzing those factors when considering whether a confession was voluntary, as the High Court requires.

"Such failures may be explained at least partly by the fact that nearly forty years have passed since the Court’s last juvenile-voluntariness case," they wrote. "Whatever the reason, reaffirmance of the Court’s holdings, and demonstration of how they are to be properly implemented, is urgently needed."

The Wisconsin Department of Justice says that Dassey's confession was voluntary and officers acted appropriately. The department argued in its petition that Dassey's attorneys were asking the Supreme Court to second-guess a state court's "reasonable application of a fact-bound, totality-of-the-circumstances test," which it has instructed lower courts not to do.